1. Technical Field of the Invention
The present invention relates generally to computerized motion detection in a series of video images, and more specifically to a system for detecting objects which are moving slowly through a visual field.
2. Background Art
Motion detection systems and methods are well known in the computer video art. However, these deal with detecting fast motion, typically for purposes of enhancing video compression between consecutive frames in a video sequence running at e.g. 30 frames per second. Objects that move sufficiently slowly through the video field will not be detected by these systems. These systems are quite good at detecting sufficiently fast motion objects, including background scenery which is e.g. blowing in the wind.
Another, unrelated type of motion detection system exists wholly outside the field of computer video or vision—building security systems which use sonar, radar, and/or infrared imaging to detect moving objects against a still, unchanging background. These systems are relatively useless in applications in which the background itself is moving, especially if the background is moving more quickly than the object to be detected. It is known that the user can adjust the sensitivity of these systems to filter out false positives caused by erroneous detection of background motion, such as trees blowing in the wind. It is also known that the user can adjust the sensitivity to suppress detection of small objects, such as a cat or a butterfly passing through the system. As a consequence, it is also known that if e.g. a burglar moves slowly enough, he will avoid detection.
What is needed is a system capable of detecting objects which are moving slowly, including those moving more slowly than the background against which they are presented.